feat(mcp): pipeline read tools

[andypalmi]

Summary

Adds Phase 1 read-only MCP tools for DevOps pipelines.

Tool file: forge/ee/lib/mcp/tools/pipelines.js

Tools added:

• platform_list_team_pipelines - GET /api/v1/teams/:teamId/pipelines
• platform_list_application_pipelines - GET /api/v1/applications/:applicationId/pipelines
• platform_get_pipeline_stage - GET /api/v1/pipelines/:pipelineId/stages/:stageId

All three tools carry readOnlyHint: true and destructiveHint: false.

Scopes allow-listed for user:expert-mcp in forge/routes/auth/permissions.js:

• team:pipeline:list
• application:pipeline:list
• pipeline:read

Closes #7696

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.42%. Comparing base (103f9ae) to head (e179669).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           feat/mcp-tools-shared-schemas    #7715      +/-   ##
=================================================================
+ Coverage                          75.41%   75.42%   +0.01%     
=================================================================
  Files                                426      427       +1     
  Lines                              22551    22563      +12     
  Branches                            5949     5949              
=================================================================
+ Hits                               17006    17018      +12     
  Misses                              5545     5545              

Flag	Coverage Δ
backend	75.42% <100.00%> (+0.01%)	⬆️

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